Aeromonas hydrophila as a Causative Agent of Fester-Needle Tail Disease in Guppies (Poecilia reticulata)

Nowadays, increases in the scale of guppy (Poecilia reticulata) breeding have been accompanied by increases in the frequency of disease, resulting in economic losses. One such disease, the fester-needle tail disease was notorious. In the current study, an epidemiological investigation was carried out for 1 year, and a total of 138 needle tail cases with obvious symptoms of rot were collected from 5 guppy farms in Anshan and Liaoyang cities in Liaoning Province, China. Microscopic observations excluded fungal and parasitic infections as causes of the disease. Transmission electron microscopy did not detect any viral inclusions in the diseased site. There was a high density of nucleiin the cells, with cells becoming longer and narrower, and containing an increasing number of vesicles. Intotal, 232 bacterial strains were isolated from fish with needle tail disease. Results of 16S ribosomal DNA sequencing, and physiological and biochemical identification showed that Aeromonasspp. accounted for 35.3% of all the isolates, with Aeromonas hydrophila being the most isolated strain; in total 37strains were isolated, accounting for 45.1% of the Aeromonas spp. isolates. A bacterial challenge experiment with A. hydrophila revealed it to be a possible causative agent of fester-needle tail disease. Histopathological observations in the controlled infection showed that epithelial cells in the caudal fin became more compacted, with all cells showing different degrees of karyotheca dissolution. These results provide a reference for further research and scientific control of needle tail disease in this economically important species.© 2021 Friends Science Publishers